1. Field of the Invention
The present invention relates to an apparatus and a method for judging the deterioration of a catalyst device and an oxygen content sensing device, in which virtual signals are generated to accurately judge the deterioration state of the catalyst device and the oxygen content sensing device by utilizing theoretical oxygen content sensing signals which are calculated in accordance with the operation state of automobiles.
2. Description of the Prior Art
Generally, in automobiles, the exhaust gas which is discharged after combustion of fuel includes harmful materials. In order to purify the harmful materials, a catalyst device is installed. Further, an oxygen content sensing device is installed for sensing the oxygen content in the exhaust gas so as to assess the air fuel ratio.
Thus, the discharge of the harmful materials is reduced by the action of the catalyst device, and the air fuel ratio in an automobile in operation is made to be accurately computed owing to the oxygen content sensing device.
In this case, if the air fuel ratio is corrected in accordance with oxygen content in the exhaust gas, then the efficiency of the catalyst device can be improved, and the fuel consumption can also be improved.
However, in the case where the air fuel ratio is corrected, the oxygen content sensing device and the catalyst device for inhibiting the discharge of harmful materials can be deteriorated due to the high temperature of the exhaust gas. Thus if the catalyst device and the oxygen content sensing device are damaged to malfunction, then the air fuel ratio cannot be accurately corrected.
Conventionally, in order to solve the above described problem, the deterioration state of the catalyst device and the oxygen content sensing device are judged, so that the air fuel ratio can be accurately corrected.
The conventional method for judging the deterioration of the catalyst device and the oxygen content sensing device will be described below.
Conventionally, a first method for judging the deterioration of the catalyst device is as follows. That is, the profusion or rarity state of the air fuel ratio, which can be judged by means of two oxygen content sensing signals which are utilized at pre-set time intervals, are counted as to its inverting times, thereby calculating an inverting frequency. The inverting frequency which is thus calculated is subjected to the calculation of an average value over a predetermined time interval. Then this value is compared with the judged deterioration value, thereby judging the deterioration of the catalyst device (utilizing the frequency ratio).
In the above described frequency ratio method, the operation conditions for the judgment of deterioration are as follows.
(1) During the time when the air fuel ratio feedback control is carried out.
(2) When the oxygen content sensor is in activation.
(3) When the output signals of an intake air sensing device lies below a pre-set level.
(4) When an idle switch is turned off.
(5) When the pre-set time has elapsed after satisfying the conditions (1) to (4).
Conventionally, a second method for judging the deterioration of the catalyst device is constituted as follows. That is, two oxygen content sensing signals are utilized to compare a pre-set value with the magnitude of the amplitudes of the sensing signals. Thus if the magnitude of the amplitudes of the sensing signals exceeds the pre-set value, then it is decided that the catalyst device has been deteriorated.
In the second method, the operation conditions for judging the deterioration are as follows.
(1) When the fuel injecting operation is not cut off.
(2) When the automobile is not put to a full load.
(3) When the air fuel ratio feedback is being controlled.
(4) When the calculated temperature of the exhaustion gas is above the pre-set level.
(5) When the oxygen content sensing device is not in an abnormal state.
(6) When a certain time has elapsed after releasing an operation prohibition.
Conventionally, a third method for judging the deterioration of the catalyst device is as follows. That is, the pre-set value and an integrated value of the oxygen content sensing signals are compared with each other so as to judge the deterioration of the catalyst device. If the integrated value is larger than the pre-set value which is set in accordance with the load state of the engine, then the catalyst device is judged to have been deteriorated.
In the above described third method, the operation conditions for judging the deterioration are as follows.
(1) When the engine speed and the temperature of the cooling water are less than the pre-set values.
(2) When the temperature of the exhaust gas is more than the pre-set value.
(3) When the automobile is not in an excessive state.
Conventionally, by using the above methods and under the above described conditions, the state of the deterioration of the catalyst device was judged, so that the air fuel ratio could be accurately maintained.
Now the conventional methods for judging on the deterioration state of the oxygen content sensing device will be described.
A first conventional method for judging the deterioration of the oxygen content sensing device is constituted as follows. That is, among the oxygen content sensing devices, when the one which is disposed in front of the catalyst device is subjected to an air fuel ratio variation for detecting the deterioration degree, the respondability of the oxygen content sensing device is utilized to make the evaluation.
In this method, during the control of the air fuel ratio feedback, a monitoring is carried out after elapsing of the setting time and after satisfying the setting conditions of engine revolution speed, volume efficiency and water temperature. If the setting conditions are not satisfied, the judging operation is terminated.
A second conventional method for judging the deterioration of the oxygen content sensing device is as follows. The variation period in which the air fuel ratio is varied to a profusion or to a rarity is measured, and thus the responding degree of the measured signals are evaluated, thereby judging the deterioration state of the oxygen content sensing device.
In the above described second method, the operation conditions for judging the deterioration degree are as follows.
(1) A region in which the oxygen content sensing device lying in the rear of the catalyst device can be controlled.
(2) A state in which the catalyst device has no abnormality.
(3) A state in which the interval for checking the operation state is irrelevant.
(4) The judgment is made after the elapsing of a certain time period from the satisfying of the above setting conditions.
A third conventional method for judging the deterioration of the oxygen content sensing device is as follows. That is, when the air fuel ratio control value is varied, the respondability of the oxygen content sensing device is judged so as to judge the deterioration of the oxygen content sensing device. Thus when the engine speed, the load state and the temperature of the cooling water satisfy the set conditions, and when a closed loop condition is relevant, the state of the oxygen content sensing device is judged.
As described above, conventionally the operating conditions of the catalyst device and the oxygen content sensing device are judged based on the various methods.
However, in the above described conventional judging methods, in the case where the operating state of the catalyst device is judged, the signals of the oxygen content sensing device which is disposed in front of the catalyst device are utilized. Therefore, if an abnormality occurs in the oxygen content sensing device which is disposed in front of the catalyst device, then the operating state of the catalyst device cannot be correctly judged.